Unidrive SP Low Voltage DC Installation Guide 13
Issue Number: 1 www.controltechniques.com
Safety Information Introduction Product information
System design
Component data Index
4.5 Important considerations and information
• It is possible to run the drive permanently in Low Voltage DC operation.
• The AC supply and DC supply must not be connected at the same time, Seamless
change-over from AC to DC or DC to AC is not possible.
• The drive must be disabled during change over of supplies.
• The DC bus must be forcibly discharged to less than the low voltage braking IGBT
turn on level or less when changing from one supply to another to ensure that the
pre-charge circuits operate correctly. If the load motor is a permanent magnet type,
steps must be taken to ensure that it is stationary or rotating slowly enough that the
emf induced in the windings is less than 25V rms.
• To achieve a reasonably short discharge time an external discharge resistor is
normally required.
• Software should not be used to interlock the supplies, discharge resistor and drive
enable. A software failure could result in hardware damage. Software may however
be used for time delays and selection logic
• All thermal overload devices used must be connected to the supply selection
interlocks, removing AC and DC supplies in the event of a device tripping.
• For Low Voltage DC operation under AC supply loss conditions; all relays and
contactors must be driven from a maintained supply.
• The system design must adhere to one of the system configurations discussed in
section 4.6 System configurations .
•Pr 6.44 indicates which supply the drive is currently operating from:
0 = Normal high voltage supply
1 = Low Voltage DC supply.
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